Wet spinning of cellulose triacetate



y 1964 J. L. RILEY 3,133,136

WET SPINNING OF CELLULOSE TRIACETATE Filed Nov. 15, 1960 2.0 Tame/r7 5PM! 5477/ Campos/770A; @ecewr Marx/wave 62 4 69/05 3,133,136 War srnsNiN-o or cincrurosn 'rniacnrarn Jesse L. Riley, Duneilen, Ni, assignor to (Celanese Con poration of America, New York, N.Y., a corporation of Delaware Filed Nov. 15, 1960, See. No. 69,367 14 Claims. (6i. 254-200) This application is a continuation-in-part of my earlier copending applications Serial No. 638,414 filed February 5, 1957 and Serial No. 730,021 filed April 23, 1958, now Patent No. 3,057,039.

This invention relates to the spinning of cellulose triacetate to form filamentary materials.

Textile materials of cellulose triacetate have recently attained considerable commercial importance. On suitable treatment, these textile materials have superior heat resistance, high safe-ironing temperatures, excellent wash fastness even When dyed in heavy shades, crease-resistance and resistance to glazing and to shrinkage on pressing with moist steam. However, the strength of the cellulose triacetate filaments used in such textile materials has not been as high as desired; Typical cellulose triacetate filaents, whether produced by dry spinning a solutionof the cellulose triacetate into an evaporative atmosphere or by wet spinning this solution into a liquid coagulant, have had tenacities of the order of 1.3 grams per denier, with elongations at break in the vicinity of 25-30%. Materials having these properties are satisfactory for use in continuous filament form, but they are not so suitable for use as staple fibers where higher strengths are desirable.

It is therefore an objective of this invention to provide novel, much stronger cellulose triacetate filamentary material and a new process for making such materials.

Another object of this invention is the provision of a new method for the wet spinning of cellulose triacetate.

Other objects of this invention will be apparent from the following detailed description and claims. In this description and claims, all proportions are by weight unless otherwise indicated.

In accordance with one aspect of this invention, a solution of cellulose triacetate in a solvent comprising methylene chloride is extruded through a spinning orifice into a non-solvent bath, hereinafter termed a spin bath, containing methylene chloride and a lower aliphatic alcohol, preferably'methanol, and the resulting swollen filamentary material is stretched in the spin bath. I have found that, for any given set of spinning conditions, there is a certain ratio of methylene chloride to the alcohol in the spin bath at which the tensile strength and elongation at break of the resulting filamentary material are both at their optimum values. That is, when curves are drawn relating tenacity and elongation, respectively to the concentration of methylene chloride in the spin bath, all other factors being the same, both curves reach their maximum values at about the same concentration of the methylene chloride, generally when the bath contains about /2 methylene chloride, or otherwise stated, when the ratio of methylene chloride to methanol is in the neighborhood of 1: 1.

The mechanical properties of the filamentary material obtained according to the process of this invention are superior to, anything heretofore attained by the wet-, dry-, or melt spinning, of cellulose triacetate. Thus, the products of this invention have tenacities ofv over, 1.8, 2 or higher, grams per denier accompanied by elongations of over 18%, e.g..20% or higher, even for filaments whose denier is in the range of 1.5. to 4. The energy of rupture, i.e. the area under the stress-strain curve from zero stretch tobreak, is high, above 800 dyne cm. for 1 cm. of a 3 denier filament. These filamentary materials are characterized by radial uniformity. This can be determined 3,.l33,l30 Patented May 12, 1064 ice by treating the filamentary materials with a saponifying agent which deesterifies the surface portions of the filamentary material, forming a cellulose skin which is then removed witha solvent for cellulose. When subjected to this treatment a filamentary material which is non-uniform exhibits difierent properties as compared with the original material, while a radially uniform mate rial has the same properties as before.

In testing for radial uniformity the surface removal can be effected, for example, by wetting the filaments to be tested in cold Water containing 0.1 gram per liter of Triton X100 (iso-octyl phenyl ether of polyethylene glycol), then immersing them in 1000 times their weight of a 50 grams per liter solution of sodium hydroxide at- C. for from 30 seconds to 3 minutes, and'quickly transferring them to cold running water for 5 minutes. The filaments are then soured in acetic acid for 15 minutes and again rinsed in running Water for 15 minutes.

After drying in air, the filaments are immersed at room temperature for 3 minutes in a solution made up of equal Weights of cupriethylene diamine and Water to dissolve the cellulose skin formed by the saponification. The filaments are then rinsed, soured, rinsed and dried as before.

The foregoing treatments of course reduce the filament.

Whereas surface removal of dry spun cellulose triacetate effects a marked increase in the rate of dyeing, surface removal of cellulose triacetate'filamentary material wet spun in accordance with the present invention does not similarly affect the dyeing rate. Thisis demonstrated as follows: Dry spun cellulose triacetate filaments of 3.75 denier when immersed in a dyebath' took up 0.18% of their weight of .dyestufi after being immersed in the dyebath for'5 minutes and 0.22% of their weight after 15 minutes immersion. If these filaments are first treated as described to remove a surface layer .44 l0- cm. thick, the filaments under identical dyeing conditions will pick up 0.22% by weight of dyestulf in 5 minutes and 0.30% in 15 minutes. This appreciable'increase in pick up vidences radial heterogeneity in the filaments.

By Way of comparison, 2.5 denier filaments produced in accordance with the invention pick up.0.24% by weight of dyestuif after being'immersed 5 minutes in the dyebath previously set forth and 0.34% after 15 minutes;

not been de-surfaced is due'to the fact that the wet spun filaments initially have a slightly pebbled surface which is smoothed out upon de-surfacing'thereby reducingslightly the surface to volume ratio of the'filaments.

In the above tests the dyebath was Water containing 50 grams per liter of dispersed Amacel Red 2B? (a red cellulose acetate dye), 1 gram per liter of Igepon T-51 (a dispersing agent) and 1 gram per liter of sodium hexa metaphosphate; the bath was'maintained at 95C. I

The 'filarnentar/ymaterials of this invention show a relatively high overall, birefringence after complete saponification (according to the technique described below) of said materials. The overall birefringence of the saponified' This slight 'de-- material is above about 0.031, typical values being in the range of about 0.034 to 0.037. This overall birefrigence is the sum of the birefringences through the fiber and is measured, in conventional manner, by a transmission technique. In the complete saponification method employed for this purpose, the filamentary material is saponified completely by immersion for at least 30 minutes in 100 times its Weight of a solution containing, by weight, 5 parts of sodium hydroxide, 12 parts of sodium acetate, parts of dimethylsulfoxide and 73 parts of water, at 80 C. Completion of saponification can be checked by wetting the filamentary material with 1 N cupriethylene diamine solution; if, as viewed under a microscope, the filamentary material dissolves completely in 30 seconds, saponification is complete; if not complete, the time of immersion in the saponifying liquor can be increased. When it has been determined that saponification is complete, the filamentary material is rinsed with distilled water until the rinse water is neutral. The saponified material is air dried,-the treatment does not cause shrinkage or loss of strength. The overall birefringence, as op posed to merely surface birefringence, is determined in customary manner, as with a Berek compensator using polarized light.

Cellulose triacetate filamentary materials produced in accordancewith this invention exhibit definite rubbery properties at elevated temperatures. This is demonstrated in the following manner: A 125 denier 40 filament yarn is held at constant length (e.g. 10 inches) and heated to a temperature of 220 C. at a just perceptible initial tension (about 0.039). The temperature is then cycled between 217 C. and 223 C. It will be found that the tension on the filament increases as the temperature increases and decreases very perceptibly as the temperature decreases, typical of a rubber. By way of comparison, if the temperature of the filament is cycled between 162 C. and 168 C., the tension will be found to decrease as the temperature increases, typical of a glass.

Like other cellulose triacetate filamentary material, the cellulose triacetate filamentary material obtained in accordance with this invention may be heat treated to raise the safe ironing temperature of fabrics produced therefrom and to improve the dimensional stability, resistance to creasing, permanence of pleating, and the like. However, the filamentary material of this invention shows substantially no shrinkage or decrease of tenacity on such heat treatment. In fact, the tenacity may even increase. For example, a filament produced in accordance with this invention and having an original tenacity of 2.15 grams per denier, when heat treated in air at 210 C. for 5 minutes shrinks less than 1% and has a final tenacity of 2.37 grams per denier.

Cellulose triacetate filamentary material produced in accordance with the invention is also characterized by resistance to creep at elevated temperatures. This is demonstrated as follows: One end of a filament is anchored within a horizontal heating tube. 10 inches from the anchored end, the filament is knotted to a glass filament which extends outside the tube and runsover a pulley. A weight is suspended from the protruding e'nd of the glass filament. With various size weights suspended from the glass filament the tube is heated and the displacement of the weight with change in temperature is noted. Cellulose triacetate filaments produced by dry spinning the initial solutions begin to creep at about 168 C. The instant filamentary materials do not creep comparably below about 178183 C. The rate and amount of creep for dry-spun filaments under a load of 0.033 gram per denier are only reached for the instant filamentary materials at a load equal to or in excess of 0.067 grams per denier.

The products are highly suitable for the manufacture of textile materials of staple fibers, as well as textile materials made of continuous filaments. The spinning procedure of this invention has given excellent results not only for the spinning of one filament from one spinnerette, but also for the spinning of thousands of parallel filaments from a single multi-apertured spinnerette.

The cellulose triacetate employed in accordance with this invention has an acetyl value of at least preferably above 61%, calculated as acetic acid. It is preferred that the intrinsic viscosity of the cellulose triacetate be in the range of about 1.5 to 3, best results being obtained when the intrinsic viscosity is at least about 2. The intrinsic viscosity" referred to above is the intrinsic viscosity of the regenerated cellulose obtained by completely saponifying, without degradation, the cellulose triacetate. The intrinsic viscosity of the regenerated cellu: lose is determined according to well-known accepted procedures, using a solution of the regenerated cellulose in cupriethylenediamine.

The cellulose triacetate is dissolved in methylene chloride either alone or, for best results, in admixture with a small amount of a lower aliphatic alcohol, preferably methanol. The proportion of methanol in the solvent mixture may be varied, up to about 15% of the solvent mixture. As for the concentration of cellulose triacetate in the spinning solution, excellent results have been obtained within the range of 18 to 26%, about 20-23% being preferred. The concentration of cellulose triacetate is desirably such that the viscosity of the solution is about 500 to 6,000 poises at the spinning temperature, i.e. the temperature at which the solution is extruded into the spin bath of methylene chloride and lower aliphatic alcohol. The spinning temperature is desirably in the range of about 15 to 45 C., though when operating at atmospheric pressure it is preferable to use a temperature below 40 C. to avoid formation of bubbles of solvent.

In accordance with one aspect of the invention it has been found that the maximum permissible spinning speed, i.e. the take-up speed beyond which spinning is unstable due to filament breakage, is dependent upon the concentration of methylene chloride in the spin bath. Advantageously this concentration ranges from about 25 to 65% and preferably from about 40 to 55%. Above the indicated range the spin bath exerts such a strong swelling action on the filaments as to interfere with rapid processing. Within the indicated range spinning speeds in excess of meters per minute can be employed without difiiculty. Below the indicated range only slow spinning is possible. For example, a 20.8% solution of cellulose triacetate, acetyl value of 61.5% calculated as combined acetic acid, in /10 methylene chloride/methanol by weight was extruded horizontally through a micron diameter circular orifice at a linear speed of 5.5 meters per minute into a spin bath containing methylene chloride and methanol in the proportions hereinafter set forth and maintained at 35 C. After travelling through the spin bath a distance of 1 meter the resulting monofilament passed about a pin so as to leave the bath and was pulled by draw rolls operated at a predetermined speed. The monofilament was dried and samples were tested for tenacity and elongation. The proportion of methylene chloride in the spin bath was varied and the peripheral speed of the draw rolls was increased to find the highest possible spinning speed, still higher speeds causing the monofilament to break during spinning. The results .are given in the following table. 7

TABLE Percent methylene chloride inthe spin bath Maximum possible spinning speed, meters per minute The optimum proportions of methylene chloride and the methanol or other lower aliphatic alcohol in the spin bath will vary depending on the temperature of spinning, other conditions of spinning being kept constant, the methylene chloride concentration being reduced as the temperature is raised and increased when the temperature is lowered. By these changes in proportions with changes in temperature the power of the bath to swell the cellulose triacetate is maintained substantially constant. In place of the methanol other alcohols, such as ethanol, n-propanol or isopropanol, may be employed, but' the results are not as good as when methanol is used.

It is found that, other conditions being the same, there is a substantially linear relationship between the temperature of spinning and the optimum concentration of methylene chloride in the spin bath. Thus, in one series of experiments, spinning 40 filaments simultaneously through orifices 0.1 mm. in diameter in a single spinnerette, the optimum spin bath at 25 C. contained 50% methylene chloride and the balance methanol; at 29 C. it contained 46% methylene chloride; and at 35 C. it contained 41% methylene chloride. Under the same conditions, but spinning 1440 filaments simultaneously from one spinnerette, at 26 C. and 32 C. the optimum spin baths contained 49.5% and 42.5% methylene chloride respectively. Plotting these data on a graph shows all these points to be substantially on one straight line. The above series of experiments was car ried out using a 21.5 solution of cellulose triacetate of acetyl value 61.5%, calculated as acetic acid, and intrinsic viscosity 2.0, dissolved in a mixture of 90 parts of methylene chloride and 10 parts of methanol, the filaments being taken up at the rate or" 75 meters per minute, at drawdown ratios of 10:1 to :1, and the denier of the resulting filaments being in the range of 2 to 4 denier per filament. Changes in conditions other than the temperature, e.g. spinning speed, acetyl value of the triacetate, etc,

may alter the exact point of optimum proportions of methylene chloride, but in general the optimum propertions of methylene chloride for any given spinning conditions will be found Within about 5% on either side of the straight line described above. Thus, in general, the

optimum proportions will be found within the range definedby the equation C=75%Ti5, where C is the concentration of methylene chloride in percent and T is the temperature in degrees centigrade.

The above proportions are on an anhydrous basis. It has been found that the addition of minor amounts of water does not interfere with the obtaining of optimum properties, though the addition of water above certain levels does affect spinning stability. For example, in one series of tests at 25 C., using a mixture of equal proportions of methylene chloride and methanol, and spinning a 3 denier filament, the addition to the spin bath of 1% and 2 /2 based on the weightof the other components of the spin bath, had little effect on the yarn properties; when the proportion of water was increased to 4% the spinning stability at higher spinning speeds was impaired, but spinning proceeded satisfactorily at lower spinning speeds, i.e. 50 meters per minute.

As stated, the filaments being extruded are stretched in the spin bath. This is done by taking up thesefilaments at a higher linear speed than the linear speed at-which 7 they are extruded. The ratio of these two speeds is known as the draw-down'ratio. A suitable range of draw-down ratios is about 15:1 to 3.5 :1, preferably 10:1 to 5:1. The actual speed of take up in the process of this invention may be quite high; for example, in excess of 75 or 100 meters per minute.

The filaments may be taken up in any desired manner, as by winding them on a driven roll, preferably after they have passed over a driven godet roll outside the spin bath. The spin bath is a good swelling agent for the cellulose triacetate and the filaments leaving the spin bath are swollen with liquid. For best results, at least a portion permitted to undergo some shrinkage in response to the loss of liquid. Such removal of liquid and shrinkage may occur for example during the passage of the filaments from the spin bath to the driven take up roll, at least a portion of the liquid being removed by evaporation during such passage. The removal of the remainder of the liquidmay be carried out in any desired manner, as by washing the filaments on the take-up roll, during and after winding, with a non-solvent such as water or isopropanol, followed b-ydrying.

The filaments produced in accordance with this invention are generally of round cross section and are bright in appearance. It will be understood that, if desired, dull filaments may be pnoduced by the incorporation of small amounts of titanium dioxideor other 'delustering agent into the spinning solution.

The accompanying drawing is a graph of the results obtained on variation of the proportions in the spin bath in Example II, below.-

The following examples are given to illustrate this invention further.

5 Example I pressure through a spinning orifice 0.1 mm. in diameter into a spin bath comprising a mixture of methylene chloride and methanol in 48:52 ratio, having a temperature of 26.8 C. The spin bath iscirculated slowly in a direction parallel to the movement of the resulting filament.

The filament travels through the bath in a generally horizontal direction for cm., then leaves the bath over a rubber guide located at thesurface of the bath, then passes through the air above the bath for 32 cm. to a second guide. made of Heanium ceramic and then passes through the air foranother 80 cm. to a chromium plated guide, from which it travels directly to a driven take up roll, on which it is wound at the rate of meters per minute. The take up roll is mounted so that its lower portion dips into a bath of water which serves to wash the filament on the roll. The resulting substantially solvent-tree 3.6 denier filament has a. tenacity of 2.0 grams per denier and an elongation of 21.5% at the break. The tension in the running filament, as measured between the Heam'um guide and theohro-miuim-plated guide is 318 mg. In this area the running filament is shrinking, despite the tension, due to evaporation of solvent. The draw-down ratio is 5.8:1.

When the above example is repeated,'excep=t that the ratio of methylene chloride to methanol in the spin bath is changed to 51:49, the resulting filament has a tenacity of only 1.4 grams per denier and an elongationot 16.5

Example 11 rate, less than 1 meter per minute, througfhthe tube. i

The resulting filaments move upward through the spin bath for a distance-of 1 meter and are then passed to gether, as a yarn, through the air for a distance of 3 meters to a take up roll on which the yarn is wound at the rate of 40 meters per minute.

This procedure is repeated, using different proportions of methylene chloride and methanol in the spin bath. The results are shown in the graphs in the drawing. As will be apparent from that drawing, the optimum tenacity and elongation are attained at about the same concentrations of'methylene chloride, i.e. 51% and the tenacity and elongation both decrease rapidly as the composition varies from the optimum.

In this example the yarn produced has a denier in the range of 2.5-3 per filament. The draw-down ratio is about 7:1.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention What I desire to secure by Letters Patent is: v

1. Process for the production of cellulose triacetate filaments which comprises extruding in filamentary form a solution of cellulose ttriacetate in a solvent therefor consisting essentially of methylene chloride and to by weight of a. lower aliphatic alcohol into a spin bath consisting essentially of a mixture of methylene chloride and a lower aliphatic alcohol, and stretching the resulting filamentary material in said spin bath, the temperature of said spin .bath lying between about 15 and 45 C. and the concentration of methylene chloride in said spin bath lying between about and 65 /4%.

2. Process as set forth in claim 1, wherein said filamentary material has a tenacity of at least 1.8 grams per denier and an elongation of at least 18%.

3. Process as set forth in claim 1, wherein said alcohol is methanol.

4. Process as set in claim 3, wherein the concentration of methylene chloride, on an anhydrous basis, in said spin bath is within the range defined by the equation of at least 1.8 grams per denier and an elongation of at 7 least 18%. Y

6. Process as set forth in claim 5, wherein said cellulose triacetate has an acetyl content of at least 61%.

7. Process asset forth in claim 6, wherein said spin a: bath is at a temperature of 25 C. and contains about of methylene chloride.

8. Process as set forth in claim 6, wherein said spin bath is at a temperature of 35 C. and contains about 41% of methylene chloride.

9. Process as set forth in claim 4, wherein said filamentary material has a tenacity of at least 1.8 grams per denier and an elongation of at least 18%, said spin bath having a swelling power for said cellulose triacetate substantially equal to the swelling power of a bath containing about 50% methylene chloride and 50% methanol at 25 C. and of a bath containing about 41% methylene chloride and 59% methanol at 35 C.

10. Process as set forth in claim 1, wherein the stretching of said filamentary material in said bath is effected using a draw-down ratio of about 10:1 to 5:1 and at least a portion of the liquid carried by the filamentary material leaving the spin bath is removed while said filamentary material is permitted to undergo shrinkage.

11. Process as set forth in claim 10, wherein the intrinsic viscosity of said cellulose triacetate is at least about 2 and the concentration of said cellulose triacetate in said solvent is about 20 to 23%.

12. Process as set forth in claim 11, wherein the water content of said spin bath is up to about 4%.

13. Process for the production of cellulose triacetate filaments which comprises extruding in filamentary form a solution of cellulose triacetate in a solvent therefor consisting essentially of methylene chloride and 0 to 15% by weight of a lower aliphatic alcohol into a spin bath consisting essentially of a mixture of methylene chloride and a lower aliphatic alcohol, and stretching the resulting filamentary material in said spin bath, the concentration of methylene chloride, on an anhydrous basis, in said spin bath lying within the range defined by the equation C=%T- -5, where C is the concentration in percent, and T is the temperature in C.

14. Process as set forth in claim 13, wherein the lower aliphatic alcohol of the solvent in which said cellulose triacetate is dissolved comprises methanol.

References Cited in the file of this patent UNITED STATES PATENTS 2,070,630 Sow-tel Feb. 16,1937

2,145,076 Ehrenstein Jan. 24, 1939 FOREIGN PATENTS 514,638 Great Britain Nov. 14, 1939 

1. PROCESS FOR THE PRODUCTION OF CELLULOSE TRIACETATE FILAMENTS WHICH COMPRISES EXTRUDING IN FILAMENTARY FORM A SOLUTION OF CELLULOSE TRIACETATE IN A SOLVENT THEREFOR CONSISTING ESSENTIALLY OF A MIXTURE OF METHYLENE CHLORIDE AND A LOWER ALIPHATIC ALCOHOL, AND STRETCHING THE RESULTING FILAMENTARY MATERIAL IN SAID SPIN BATH, THE TEMPERATURE OF SAID SPIN BATH LYING BETWEEN ABOUT 15 AND 45*C. AND THE CONCENTRATION OF METHYLENE CHLOIRIDE IN SAID SPIN BATH LYING BETWEEN ABOUT 25 1/4 AND 65 1/4%. 